Sunlight is an abundant, clean, renewable, and free energy resource. Current photovoltaic technologies for converting sunlight into electricity have relatively low efficiencies in the range of 5% to 20%, and at best 40% or so for high-performance triple junction PV cells. Other recent attempts include conversion of sunlight into electricity by coupling resonant dipole-like antenna structures at the nano-scale to fast acting diodes for rectifying sunlight-induced electrical fields into electricity (referred to as “rectenna systems”). However, such efforts to develop rectenna systems have fallen significantly short of the desired result, with observed conversion efficiencies around 1% at best. See, B. Berland, Photovoltaic Technologies Beyond the Horizon: Optical Rectenna Solar Cell”, NREL Contract No. DE-AC36-99-GO10337, NREL/SR-520-33363, September 2002.
The principle limitation discovered by rectenna investigators was the poor construction of a metal-insulating-metal (MIM) rectifying diode. The diode needed to have an asymmetric current-voltage characteristic, but this was found to be very difficult to achieve in practice. This severely limited the ability of the diodes to perform rectification of the electrical fields of light presented to it from the antenna. Furthermore, a low diode capacitance and properly designed resistance and inductance were needed for optimal impedance matching of the antenna structure to the diode. The added complications of quantum effects severely hampered the development of nano-scale resonant antennas. Quality impedance matching requires control of the shape of the antenna to within 1/100 of the characteristic size of the antenna—a feat hard to achieve for visible wavelength scale antennas. These prior efforts depended more on extending hybrid microwave methods and techniques, rather than more suitable quantum mechanical methods and techniques.